| 摘要 |
PROBLEM TO BE SOLVED: To provide a serial bus system for using correspondent equipment connected to a low-order port while switching it for plural host systems. SOLUTION: When a serial bus cable 1a from a host system 1 is connected to a high-order port 3, 5V is supplied from the host system 1 through a power line 3a to a judging circuit part 5 and this judging circuit part 5 monitors the supply of 5V from a high-order port part 4. When there is no supply of 5V from there, an initial setting signal 6a from a selector circuit part 6 and a host system switching signal 7a from a sense circuit part 7 are ignored, only the host system 1 connected to the high-order port 3 is continuously selected, and serial bus data signal lines 5b and 5c are connected to a control circuit part 8. Therefore, the judging circuit part 5 watches the initial setting signal 6a from the selector circuit 6 and judges which one of host systems 1 and 2 is to be defined as a primary host system.
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